Pressure and temperature sensor

ABSTRACT

The invention pertains to a pressure and temperature sensor, in particular for determining a pressure and temperature condition in a cavity of an injection molding apparatus or the like having a pressure body which co-operates with a sensor housing and which in a mounted condition can be acted upon by a pressure in the cavity and which is intended for transmitting the pressure to a piezoelectrically acting sensor arrangement, wherein an electrical signal generated by the sensor arrangement as a reaction to the pressure is taken out of the sensor housing by means of an electrical contact device, wherein a thermoelectric detector element is fitted in the pressure body and an electrical temperature signal generated by the detector element is taken out by way of the electrical contact device.

The invention concerns a pressure and temperature sensor, in particularfor detecting a pressure and temperature condition in a cavity of aninjection molding apparatus or the like.

Sensors of that kind are used in particular when measuring the internalpressure in a tool in an injection molding apparatus, the pressure ofmolten material in pressure chambers of a corresponding installationbeing directly or indirectly detected.

During such an injection molding procedure an internal pressure patternwhich is dependent on a respective state in the process obtains in thepressure chamber (cavity)—from a sharp rise after the beginning of theinjection procedure by way of a more or less shallow pressure dropduring the post-pressure phase down to atmospheric pressure. In thatrespect in particular parameters of a plastic material to be injected,the injection rate or the temperature conditions in the interiorinfluence the configuration of that curve. Therefore, it is precisely inrelation to high-precision parts that accurate reproducible measurementof the pressure conditions in an injection molding pressure cavity is animportant consideration in order to be able to aid and support thecomplex control procedures which are necessary to achieve an optimumresult.

In that respect it has been found desirable to be able to measure thetemperature in the internal cavity, in addition to the pressure therein.More specifically, such an additional parameter would then make itpossible to support and aid in particular still further controlprocedures which are pressure-neutral and to that extent cannot bemonitored and controlled by pressure measurement alone.

It is known in that respect for temperature detection to be additionallyprovided in the internal cavity in locally separate relationship from aconventional pressure sensor in order to acquire that further controlparameter.

Besides the mechanical and structural complication and expenditure whichhowever is inevitably necessary for that purpose (thus for example asecond access would have to be provided to the pressure chamber),pressure and temperature measurement values from such an arrangementalso mean that the temperature is measured at a different location froma respective pressure. Particularly in the event of severelynon-homogenous conditions in the internal space therefore there canpotentially be incorrect measurements and, as a result thereof,malfunctions.

Therefore the object of the present invention, in particular forparameter detection in an internal space of injection moldingapparatuses, is to provide a sensor of the general kind set forth forpressure and temperature detection, which is also easily suitable at lowcost for conventionally existing injection molding apparatuses that areonly designed for pressure measurement, and which permits locallyinterrelated pressure and temperature measurement.

Advantageously, the thermoelectric detector element which is directlyfitted into the pressure body permits local detection of the temperaturedirectly at the location of pressure measurement without additionalprecautions having to be taken in the pressure chamber or for examplewithout the diameter of a sensor having to be increased. The inventionalso advantageously provides that arranging for temperature detection inthe pressure body itself and thus in the immediate vicinity of thetemperature source means that it is possible to implement quicklyreacting, short-time temperature detection which is necessary inparticular for process operations which themselves are relatively short.

Advantageous developments of the invention are claimed in the appendantclaims.

Thus in a particularly preferred feature the pressure body is of acircular cross-section and is dimensioned for use in openings of adiameter for example of 4 mm, which are already present for conventionalpressure sensors. That makes it possible for existing injection moldinginstallations to be converted in a particularly simple fashion.

It has also proven to be advantageous to use flat crystal elements inthe form of wafers as detector elements as that makes it possible tooptimize the electrical pressure signal.

Choosing the thermoelectric sensor element in the form of a casing orjacket-type thermocouple element also permits complete capacitivescreening which is appropriate in particular in regard to the adjacentpressure detection.

In accordance with a preferred development moreover the thermocoupleelement is designed to be exposed in the pressure-application surface.That makes it possible further to minimize the thermal response time.

In order to provide for contact-sure contacting which is howevernonetheless simple to produce in respect of a pressure and temperaturesensor according to the invention, it is particularly appropriate forthe contact device to be in the form of a coaxial plug connection, inwhich case it can preferably also be of multi-shellstructure—corresponding to the number of electrical poles to be takenout of same—, or a shell of a plurality of poles is used for contactingpurposes.

Further advantages, features and details of the invention will beapparent from the description hereinafter of embodiments by way ofexample and with reference to the drawing in which:

FIG. 1 shows a perspective view of the pressure and temperature sensoraccording to the invention,

FIG. 2 is a view in axial section through the pressure and temperaturesensor according to the invention in a first embodiment, and

FIG. 3 is a view in axial section through the pressure and temperaturesensor according to the invention in a second alternative embodiment ofthe invention.

The sensor 10 which is intended in particular as an internal pressureand temperature sensor for direct measurement of the pressure of moltenmaterial in an injection or casting tool has a cylindrical sensorhousing 12 of steel, which at the pressure side co-operates with acylindrical pressure rod body or plunger 16 as a pressure element. Therod 16 which in the illustrated embodiment by way of example is about 4mm in outside diameter is compressively elastically connected to thesensor housing 12 by way of a steel prestressing sleeve 18 which engagesover a projection 14 and in its central region has a thin deformationlocation 20 which permits elastic deformation.

A plug portion 22 is provided at the end of the sensor housing 12, whichis opposite to the pressure rod 16.

The sensor arrangement 10 is fixed to the cavity or to the desiredlocation in the injection space by means of a union nut (not shown inthe drawing) or the like fixing member—with a front annular shoulder 24and a rearward annular shoulder 26 respectively on the housing 12 assupport means.

A feed conduit 25 which is taken out rearwardly (with respect to thepressure direction) leads electrical connections of the detectionelements provided in the sensor unit to an electronic detection andevaluation unit (not shown) which can be connected thereto.

As shown in detail in FIG. 2 the transitional region between thepressure rod 16 and the housing projection 14 on the sensor housing, thetransitional region being enclosed by the deformation location 20 of thesleeve 18, comprises an arrangement of various plate-shaped elementswhich extend substantially radially symmetrically about a longitudinalaxis through the sensor arrangement: a contact plate portion 30 ofconducting material is delimited on both sides by first and secondquartz wafers 32 and 34 respectively so that the mutually facingsurfaces of the quartz wafers 32, 34 respectively contact the centralcontact plate portion 30 while the respective mutually remote sides ofthe quartz wafers 32, 34 electrically conductingly contact the pressurerod 16 and the housing projection 14 on the sensor housing 12.

A sheath-shaped insulating ring 36 of Teflon material or ceramicencloses the arrangement formed from the first quartz wafer 32, thecontact plate portion 30 and the second quartz wafer 34 and thus formsinsulation relative to the surrounding sleeve 18.

The arrangement of the first quartz wafer 32, the contact plate portion30 and the second quartz wafer 34 also has a central opening 38 forsignal lines—which are to be described in greater detail hereinafter—forthe thermocouple element 40 arranged in the pressure rod 16 to be passedtherethrough.

In that way an electrically conducting ground connection can then bemade between the rod 16 and the housing 12 by way of the metal sleeve18; at the same time, the action of the insulating sheath 36 ofinsulating material provides for insulating both the contact plateportion 30 and also each peripheral surface of the quartz wafers 32, 34with respect to that ground potential.

Such an arrangement affords an electrical parallel connection of the twoquartz wafers 32, 34, wherein the contact plate portion 30—connected tothe respective, mutually facing surfaces of the quartz wafers—acts inthat respect as a common signal contact for charges which are to begenerated by the quartz wafers 32, 34, while the respective mutuallyremote sides of the quartz wafers are connected in parallel relationshipto ground.

The contact or signal plate portion 30 is connected by way of a contactconnection or terminal 42 to a pressure signal line 44 which in turn hasan electrical insulating sheath (insulating tube) 46.

The electrical pressure signal line 44 is taken as far as a receivingmeans 48 for a contact needle 50 in the plug portion 22 and is connectedthereto so that the contact needle 50 carries the electrical potentialwhich occurs at the signal plate portion 30.

The receiving means 48 for the contact needle 50 is surrounded in theinterior of the plug by an insulating sleeve 52 of Teflon(alternatively: for example ceramic) which in turn is peripherallysurrounded in positively locking relationship by a cylindrical contactsleeve 54. A further, outer insulating sleeve 56 which encloses thearrangement formed by the contact needle receiving means 48, the innerinsulating sleeve 52 and the cylindrical contact sleeve 54 is thenfitted at its peripheral side into a suitable longitudinal bore in thesensor housing 12. At the peripheral side the outer insulating sleeve 56is surrounded in the region of the plug portion 22 by a plug edge 58which is formed integrally with the sensor housing 12 and which over apart of its peripheral surface has a male screwthread portion 60.

In that way, provided on the plug side is a rotationally symmetrical,multi-shell plug structure which from the outside inwardly has a groundconnection (plug edge 58), an insulation (outer sleeve 56), a contactsleeve for the temperature signal (sleeve 54) and a central contactneedle 50 for the pressure signal. Jointly with pressure detection, thesecond pole of the thermocouple element is also taken by way of thecommon ground.

To describe this in greater detail, the thermocouple element 40 which isaccommodated in the pressure rod 16 has a first thermoelectric wire(diagrammatically indicated by reference 62) which is taken from an endconnecting location 64 to a ground contact 66 at the inner end of thepressure rod 16. A second thermoelectric wire 68 extends from theconnecting location 64 substantially axially through the pressure rod16, through the opening 38 formed in the arrangement 32, 30, 34 andthrough the sensor housing 12 to the plug portion 22 where an electricalconnection is made between the second thermoelectric wire 68 and thecylindrical contact sleeve 54 (by clamping between the sleeve 54 and thesurrounding insulating sleeve 56). In that arrangement, the secondthermoelectric wire 68 is sheathed by an electrical insulation 70, overpractically its entire length.

As shown in FIG. 2, the thermocouple element 40 is arranged in the rodregion 16 in such a way that the connecting location 64 of thethermocouple element is at a spacing from the outside wall 72 (which inthe assembled condition contacts the temperature or pressure mediumrespectively) of the pressure rod 16. The thermocouple element 40 isalso relieved of pressure in a direction towards the disk arrangement32, 30, 34 through the opening 38 which is of a slightly larger diameterthan the thermocouple element.

O-rings 74 provided on the housing 12 and on the rod 16 respectivelythen also serve for adaptation and mechanical sealing.

For practical use, pressure and temperature sensors (also referred to aspT-sensors) are fixed to the pressure space for example of an injectionmolding machine—for example in the cylinder head or to a hot channel orrunner—in such a way that the outside wall 72 of the pressure rod 16extends into the respective pressure space or is aligned with a pressurespace wall.

During an injection molding procedure varying pressure conditions willthen occur at the injection tool, as a functional pattern which istime-dependent, in which respect it is particularly important to detectthe pressure phases “injection” and “dwell pressure” and to use them asinput parameters for pressure control purposes.

At the same time, a positionally accurate temperature signal isavailable by virtue of the output signal of the thermocouple element 40.That temperature signal furnishes a respective temperature value in thepressure space or chamber—at the same location as the pressuremeasurement—as a supplementary parameter for the process controloperation. In practical use pressures of up to about 2000 bars can occurat temperatures of between 250 and 400° C. in the case of plasticmaterial injection molding procedures. In that respect, the illustratedarrangement not only permits precise measurement value detection withshort reaction times (when using a jacket or casing type thermocoupleelement, only a few ms response time) under the extreme conditionsindicated; in addition the compact arrangement of temperature detectionin the pressure body itself makes it possible to use previous openingsor mountings for conventional pressure sensors (for example for thediameter of 4 mm), without the need for separately taking precautions orimplementing conversion steps for additional temperature measurement.

Practical use of the pressure and temperature sensor according to theinvention also exhibits excellent properties in regard toreproducibility of the pressure and temperature values so that theinvention is particularly suitable for demanding and complex controlapplications. Not least the additional temperature detection, forexample at the injection channel or runner, permits substantially moreprecise process control which for example also embraces materialspecifics, with optimum local accuracy and local coincidence of pressureand temperature values.

FIG. 3 shows a slightly modified, alternative embodiment for thetemperature and pressure sensor of FIG. 2.

While the thermocouple element of FIG. 2, in relation to the outsidewall 72 pressure-application surface at the pressure side, is arrangedconcealed in the pressure rod 16. FIG. 3 shows an embodiment with ajacket or casing thermocouple element 76 which extends into a pressurespace or chamber, by virtue of being fitted into the outside wall 72 atthe front, welding and grinding away to be flush with the outside wall.

Furthermore, in the embodiment of FIG. 3, the pole on the ground side ofthe thermocouple element (thermoelectric wire 62) is not contacted inthe region of the pressure rod 16 and thus taken to ground, but togetherwith the signal-carrying second thermoelectric wire 68 it is takenthrough a capacitively screening guide 78 to the plug portion 22. Therethe second thermoelectric wire 68 is then connected to the cylindricalcontact sleeve 54 in the manner already described above while the groundfeed of the thermocouple element 76 only acquires a ground connection inthe region of the plug portion 22 by virtue of being clamped between theouter insulating sleeve 56 and the sensor housing 12.

In particular the embodiment of FIG. 3 therefore affords a constructionwhich enjoys better capacitive screening and which advantageouslyprotects the high-resistance pressure signal from interferenceinfluences.

The thermocouple element described with reference to FIG. 3 involves anNi/NiCr-casing thermocouple element with a screening metal casing 78which is passed in the manner shown in FIG. 3 through the rod 16 and thehousing 12 respectively to the plug portion.

While moreover in the described embodiment shown in FIG. 3, one pole ofthe casing-type thermocouple element is grounded, in accordance with afurther alternative embodiment (not shown) it is possible for the twopoles of the casing-type thermocouple element to be afforded separatelyin order not to involve a damaging voltage drop and to be able to effectmore precise evaluation of the thermoelectric voltage between thethermoelectric wires themselves. Such a configuration could be forexample such that the cylindrical contact sleeve 54 carrying thethermoelectric signal could be divided into a two-pole configuration inthe peripheral direction and a respective contact portion produced inthat way could be connected to an associated pole of the thermocoupleelement. A suitably externally communicating plug would then be able totake off both thermocouple element feed lines, independently of ground.

While the above-described embodiments have preferably used a casing-typethermocouple element as the temperature sensor, in principle othersensors are also suitable, for temperature detection in the pressure roditself and for producing a signal which is to be appropriatelyelectrically taken off, besides the pressure signal.

The pressure sensor arrangement is also not limited to the describedembodiment; it would also be possible for example to use a plurality ofmodules of piezoelectric disks or wafers—for example 6 or 10—or afundamentally different pressure detection principle.

The present invention is also not limited to the coaxial connectionconfiguration illustrated in the described embodiments; on the contraryit is a matter for the discretion of the man skilled in the artaccording to the requirements involved to implement a suitable plugconstruction and design which affords both simple manufacture andconnection and also contact security and screening.

What is claimed is:
 1. A pressure and temperature sensor for detecting apressure and temperature condition in a cavity, comprising a pressurebody (16) which co-operates with a sensor housing (12) and which in amounted condition can be acted upon by a pressure in the cavity andwhich is intended for transmitting the pressure to a piezoelectricallyacting sensor arrangement (30, 32, 34), wherein an electrical signalproduced by the sensor arrangement (30, 32, 34) as a reaction to thepressure is passed out of the sensor housing (12) by means of anelectrical contact device (48, 50, 52, 54, 56, 58), characterized inthat a thermoelectric detector element (40) is fitted in the pressurebody (16) and an electrical temperature signal produced by the detectorelement (40) is passed out by way of the electrical contact device (48,50, 52, 54, 56, 58); said thermoelectric detector element (40) islocated adjacent to said sensor arrangement (30, 32, 34) in saidpressure body (16) such that the temperature can be measured atsubstantially the same location where pressure is measured.
 2. A sensoras set forth in claim 1 characterised in that the pressure body is inthe form of a substantially cylindrical pressure rod.
 3. A sensor as setforth in claim 2 characterised in that the pressure rod is of an outsidediameter of about 4 mm.
 4. A sensor as set forth in claim 3characterised in that the sensor arrangement has at least onepiezoelectric crystal wafer which co-operates by way of a flat side withthe pressure body (16).
 5. A sensor as set forth in claim 4characterised in that the thermoelectric detector element is in the formof an elongate casing thermoelectric element.
 6. A sensor as set forthin claim 5 characterised in that the pressure body (16) includes apressure-application surface (72); one end of the thermoelectricdetector element is exposed in said pressure-application surface (72)substantially flush therewith.
 7. A sensor as set forth in claim 6characterised in that the thermoelectric detector element has acapacitive screening which is operative in relation to the pressure body(16), the sensor arrangement (30, 32, 34) and the sensor housing (12).8. A sensor as set forth in claim 7 characterised in that a feed linefor the thermoelectric detector element is passed through an openingformed substantially centrally in the sensor arrangement.
 9. A sensor asset forth in claim 8 characterised in that the electrical contact deviceis in the form of a plug with at least one coaxial contact sleeve at theside of the sensor housing which is opposite to the pressure body.
 10. Asensor as set forth in claim 9 characterised in that electricalconnections of the thermoelectric detector element are passed outground-free and separatedly by way of the electrical contact device. 11.A sensor as set forth in claim 10 characterised in that saidthermoelectric detector element includes two thermoelectric wires (62,68); said two thermoelectric wires (62, 68) of said thermoelectricdetector element are passed out in the form of contact surfaces of acommon contact sleeve of the contact device.
 12. A pressure andtemperature sensor for detecting a pressure and temperature condition ina cavity comprising a pressure body (16) which co-operates with a sensorhousing (12) and which in a mounted condition can be acted upon by apressure in the cavity and which is intended for transmitting thepressure to a piezoelectrically acting sensor arrangement (30, 32, 34),wherein an electrical signal produced by the sensor arrangement (30, 32,34) as a reaction to the pressure is passed out of the sensor housing(12) by means of an electrical contact device (48, 50, 52, 54, 56, 58),and wherein a thermoelectric detector element (40) is fitted in thepressure body (16) and an electrical temperature signal produced by thedetector element (40) is passed out by way of the electrical contactdevice (48, 50, 52, 54, 56, 58), characterised in that a transitionalregion comprising the sensor arrangement, between the pressure body (16)and a housing projection of the sensor housing, is enclosed by a sleeve(18); means for connecting the pressure body (16) to the sensor housingin a pressure resilient manner.